South American bowl (indigenous)background ?

I found this at garage sale over 9 yrs ago lady told me she got it from South America I'm not sure if it's from an indigenous tribe or not I vaguely remember her telling me something about its origins it's very heavy I wish I had of got more details it's over 60cm in length an 27cm at its widest spot she said to oil it up as it brings out the natural earth colours it's made from clays I guess don't know of precise mix